The present invention is directed to a full function valve for an anti-lock brake system, and more particularly, to a full function valve for an anti-lock brake system that includes improved portings for ease of mounting the valve.
A conventional anti-lock brake system (xe2x80x9cABSxe2x80x9d) monitors the wheels of a vehicle during braking and institutes corrective action when the one or more of the wheels begin to slip or lock up. When a wheel begins slipping, the ABS reduces the pressure applied by the brake of that wheel. Once the wheel begins turning again, the system gradually reapplies the pressure in the brake until the wheel begins slipping again. A specially designed ABS valve is utilized to implement this control algorithm.
A typical prior art braking system is shown in FIG. 1 and includes a master cylinder 1 that supplies pressurized brake fluid to a set of brakes 2, 3 in response to pressure applied the pedal 4. The increase in pressure in the brakes 2, 3 causes the brakes to apply a decelerating torque on associated wheels 5, 6. The braking system also includes an accumulator 7 that receives brake fluid that is bled from the brakes 2, 3 to reduce the braking torque applied by the brakes. The ABS valves 8, 9 are coupled to the brakes 2, 3, to the master cylinder 1 and to the accumulator 7. Each of the valves 8, 9, includes a normally open valve portion 11 and a normally closed valve portion 13. Each of the valves 8, 9 has three states: (1) the apply state (i.e. normal braking), in which pressure conveyed by brake fluid from the master cylinder 1 is transmitted to the brakes 2, 3 to cause the brakes to apply braking torque to the associated wheels 5,6; (2) the release state, in which pressure is bled from brakes 2, 3 to the accumulator 7 to reduce the braking torque applied to the associated wheels; and (3) the hold state, in which the pressure in the brakes (and thus the applied braking torque) is held at a relatively constant level.
When the valves 8, 9 are in the apply state, the normally open.valve portions 11 are open (i.e. unactivated) and the normally closed valve portions 13 are closed (i.e. unactivated). When the braking system is in the release state, the normally open valve portions 11 are closed (activated), and the normally closed valve portions 13 are open (activated). When the system is in the hold state, the normally open valve portions 11 are closed (activated), and the normally closed valve portions 13 are closed (unactivated).
Typical full function ABS valves include a normally open valve portion and a normally closed valve portion mounted in a single longitudinal body. The normally open and normally closed valve portions are typically actuated by a single coil and are axially spaced from each other along the length of the valve body. The valve body includes three ports: a port to the master cylinder, a port to the brake, and a port to the accumulator.
U.S. Pat. No. 3,970,111 to Brxc3xcne et al. discloses a conventional electromagnetic 3-way valve arrangement having two valve portions for use in an ABS. The valve includes ports for the master cylinder, accumulator, and brake. The ports for the accumulator and for the brake are located on one end of the valve body, and the port for the master cylinder is located on the opposite end of the valve body. Because the ports for the accumulator and the brake are located adjacent to each other and they may be received in a standard ported block. However, a separate line must be run to connect the master cylinder port of the valve body to the master cylinder. Thus, for example, a tube or other conduit must be run externally of the valve to the pressure source. This external tubing increases the required connections and complexity of the valve system. Accordingly, there is a need for a full function valve for use in an ABS wherein all of the connections for all three ports are located on one end of the valve such that the valve may be received in a block that completes all of the fluid connections.
The present invention is a full function valve for use in an ABS wherein the ports for the master cylinder, accumulator and brake are all located on one end of the valve, which reduces the required connections and the overall complexity of the valve. In particular, because all of the ports are located at one end of the valve, the valve can be received in a block that acts as a manifold to connect all of the ports to the associated components. This eliminates the use of any external tubing, and keeps all connections to and from the normally open valve portion and the normally closed valve portion internal to the valve body.
It is important to guide the fluid within the valve without disrupting the magnetic flux paths that are required to activate the valve portions since the normally open valve portion is axially spaced from the normally closed valve portion. The present invention includes fluid path arrangements, as well as a magnetic body, both of which minimize disruptions of magnetic flux paths.
In a preferred embodiment, the present invention is a full function antilock brake valve which includes a master cylinder port, a wheel port and an accumulator port. The valve includes a first fluid path coupling the wheel port and the master cylinder port and a second fluid path coupling the wheel port and the accumulator port. The valve has a normally open valve portion for controlling the flow of fluid through the first fluid path, and the normally open valve portion includes an armature having a plunger that engages a seat. The first fluid path includes an inflow portion that delivers flow from the wheel port to the normally open valve portion. The valve further includes a normally closed valve portion for controlling the flow of fluid from the wheel port to the accumulator port, the normally closed valve portion including an armature having a plunger that engages a seat. The valve further comprises a coil located radially outwardly of the normally open valve portion and the normally closed valve portion such that the coil controls the actuation of the normally open valve portion and the normally closed valve portion when sufficient current is passed through the coil. At least part of the inflow portion of the first fluid path is located radially inside the coil.
Accordingly, it is an object of the present invention to provide a full function ABS valve which is easy to connect to an ABS system; an ABS valve which includes all three ports at one end of the valve; and an ABS valve which reduces the secondary air gaps in the valve.
Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings and the appended claims.